Pyrotechnic actuator

ABSTRACT

The invention relates to an actuator comprising an actuator element movably supported at an actuator housing, a pyrotechnic pressure element to move the actuator element and a control means to control a force exerted onto the actuator element by the pressure element to move the actuator element.

FIELD OF THE INVENTION

The invention relates to an actuator comprising an actuator elementmovably supported at an actuator housing and a pyrotechnic pressureelement to move the actuator element.

BACKGROUND OF THE INVENTION

An actuator of this type is generally known and is used, for example, tointerrupt electrical connections or to trigger fast switchingprocedures, e.g. in the motor vehicle safety sector.

The pyrotechnic pressure element, which is also called a pyrotechnicigniter in the case of an electrical activation, has the advantage inaddition to a particularly fast power development that the energyrequired to move the actuator element can be stored without pressureover a long period of time by means of suitable chemical substances andcan be released as required by means of a comparatively small electricalor mechanical energy.

An activation of the pressure element triggers a conversion of thechemical substances and results in the generation of a pressure impulseby which the actuator element is moved relative to the actuator housing,e.g. is pushed out of it. Since the action on the actuator element takesplace very abruptly, the actuator element is moved in a short time andin an uncontrolled manner from a starting position into an end position.

This fast and uncontrolled movement of the actuator element has provedto be disadvantageous in those applications in which the movementprocedure of the actuator element should endure for a specific timeand/or a bounce of the actuator element should be avoided, e.g. inlocking or unlocking processes.

It is the underlying object of the invention to provide a pyrotechnicactuator, wherein the movement of the actuator takes place in acontrolled manner.

An actuator having the features of claim 1 is provided to satisfy thisobject.

The actuator in accordance with the invention comprises an actuatorelement movably stored at an actuator housing, a pyrotechnic pressureelement for the movement of the actuator element and a control means forthe control of a force exerted onto the actuator element by the pressureelement to move the actuator element.

The force exerted on the actuator element on a triggering of thepressure element can be set by the control means such that the movementof the actuator element takes place at a desired speed. The controlmeans is in particular adjustable such that the movement of the actuatorelement takes place over a desired period and/or a bounce of theactuator element is avoided. A defined movement of the actuator elementcan therefore be pre-set by the control means and a matching of theactuator to its respective area of use is possible.

Advantageous embodiments of the invention can be seen from the dependentclaims, from the description and from the drawing.

SUMMARY OF THE INVENTION

In accordance with a preferred embodiment, the control means is arrangedbetween the pressure element and the actuator element. It is therebyachieved that the gas pressure generated by the pyrotechnic pressureelement does not build up abruptly, but increasingly in front of asurface of the actuator element which is to be acted on. Thiscontributes to a yet more controlled movement of the actuator element.

The control means advantageously includes a diaphragm. This represents aparticularly simple form of a control means. On an activation of thepressure element, a high-pressure system is created in front of thediaphragm, i.e. on the pressure element side of the diaphragm, and alow-pressure system is created behind the diaphragm, i.e. on theactuator element side of the diaphragm. By a suitable selection of thediaphragm cross-section, the pressure build-up in the low-pressuresystem, i.e. the pressure increase gradient, and thus ultimately theresulting force acting on the actuator element, can be set. In otherwords, the cross-section of the diaphragm forms a control parameter ofthe control means.

The diaphragm is preferably integrated into a spacer means for thepressure element. The spacer means serves for the correct positioning ofthe pressure element in the actuator housing. The spacer means satisfiesa dual function by the simultaneous integration of the diaphragm,whereby the number of the components is reduced and the design of theactuator is simplified.

In accordance with a further embodiment, grouting is provided for thepressure element. In the event of an activation of the pressure element,the grouting brings about a more uniform conversion of the chemicalsubstances contained in the pressure element and thus results in a moreuniform gas pressure. Ultimately, a more uniform action on the actuatorelement and consequently an even more controlled movement of theactuator element is thereby achieved.

In accordance with an advantageous embodiment, the actuator element isfixed in a starting position by a grouting element. The grouting elementsatisfies a dual function in that it forms grouting for the pressureelement, on the one hand, and provides a fixing of the actuator element,on the other hand. The design of the actuator is thereby simplified evenfurther.

The grouting element preferably has a shear section which cooperateswith the actuator housing such that a substantial movement of theactuator element relative to the actuator housing is only possible aftera shearing of the shear section off the grouting element. For example,the shear section can be supported at a shoulder of the actuator housingin a starting position of the actuator element.

Due to the shear section, the actuator element is not set in motionimmediately on an activation of the pressure element, but a pressuremust first build up at the side of the actuator element to be acted on,said pressure being sufficient to shear off the shear section of thegrouting element. A force threshold is created in this manner belowwhich no movement of the actuator element takes place. It is therebyensured that the force which acts on the actuator element and which theactuator element can in turn apply is not lower than a minimum force.

In accordance with a further advantageous embodiment, a holding deviceis provided to hold the actuator element in an end position after amovement by the pressure element. The holding device has the effect thatthe actuator element cannot be simply returned back into its startingposition from its end position after a triggering of the actuator. Inother words, the movement of the actuator element is irreversible.

The holding device can include a knurling of the actuator element whichis pressed into a bore of the actuator housing on a movement of theactuator element. Alternatively or additionally, the holding device caninclude a friction-retaining slope of the actuator housing in which theactuator element jams on its movement. Both variants represent aparticularly simple form of a holding device for the actuator elementand thus contribute to a simple design of the actuator.

The actuator element is preferably formed by a piston displaceablysupported in the actuator housing. Generally, however, other designs ofthe actuator element are also conceivable; the actuator element coulde.g. be made in the manner of a lever and could be pivoted in the eventof a triggering of the pressure element.

DESCRIPTION OF THE DRAWINGS

The invention will be described in the following purely by way ofexample with reference to advantageous embodiments and to the encloseddrawing. There are shown:

FIG. 1 a cross-sectional view of a first embodiment of the actuator inaccordance with the invention in a starting state;

FIG. 2 a cross-sectional view of the actuator of FIG. 1 in a triggeredstate;

FIG. 3 a cross-sectional view of a second embodiment of the actuator inaccordance with the invention in a starting state;

FIG. 4 a cross-sectional view of the actuator of FIG. 3 in a triggeredstate;

FIG. 5 a cross-sectional view of a third embodiment of the actuator inaccordance with the invention in a starting state;

FIG. 6 a cross-sectional view of the actuator of FIG. 5 in a triggeredstate;

FIG. 7 a cross-sectional view of a fourth embodiment of the actuator inaccordance with the invention in a starting state; and

FIG. 8 a cross-sectional view of the actuator of FIG. 7 in a triggeredstate.

DETAILED DESCRIPTION OF THE INVENTION

A first embodiment of the pyrotechnic actuator in accordance with theinvention is shown in FIGS. 1 and 2.

The actuator has an actuator housing 10 in which a pyrotechnic pressureelement 12 is arranged. The pressure element 12 is held by a pressureelement carrier 14 in a rear region, a lower region in the Figure, ofthe actuator housing 10.

For the correct positioning of the pressure element carrier 14 in theactuator housing 10, a beaker-shaped spacer cup 16 is provided whoseopen side faces the pressure element carrier 14 and which surrounds thepressure element 12 at least regionally. The pressure element carrier 14is fixed to the actuator housing 10 by means of a clinching connection18.

Ignitable chemical substances are contained in the pyrotechnic pressureelement 12 and can be brought to reaction, for example by electricalenergy, on a triggering of the pressure element 12. Pressure elements ofthis type and suitable ignition mechanisms are sufficiently known.

A gas pressure impulse is created in the pressure element 12 by a fastconversion of the chemical substances and opens a cylindrical sleeve 20of the pressure element 12 projecting into the spacer cup 16. Desiredbreak points, e.g. in the form of stampings, are provided at the endface 22 of the sleeve 20 to ensure an opening of the sleeve 20 at theend face.

The pressure element 12 serves for the actuation of an actuator element24 which is arranged in a front region, an upper region in the Figure,of the actuator housing 10. The actuator element 24 has the shape of apiston which is supported displaceably in the axial direction in theactuator housing 10.

The piston 24 includes a cylindrical main section 26 which is guided ina bore 30 provided at a front end face 28 of the actuator housing 10. AsFIG. 1 shows, a front end face 32 of the piston 24 terminates in a flushmanner with the front end face 28 of the actuator housing 10 in thestarting state of the actuator.

In the region of the rear end of the main section 26, the piston 24 hasa disk-shaped head section 34 which is guided, in a starting position ofthe piston 24, by a wall section 36 of the actuator housing 10 andterminates with it in a substantially gas-tight manner (FIG. 1).

When the pressure element 12 is ignited, a gas pressure is built up inthe pressure element 12 by the reaction of the chemical substanceslocated in the pressure element 12 which results in an opening of thesleeve 20 of the pressure element 12. The gas created can flow out ofthe pressure element 12 through the opening of the sleeve 20 and buildup a gas pressure in a space 38 bounded by the spacer cup 16 and thepressure element 12 or the pressure element carrier 14.

As FIG. 1 shows, the piston head section 34 is disposed at a base 40 ofthe spacer cup 16 in the starting position of the piston 24. An opening42 is provided in the base 40 of the spacer cup 16 through which the gasgenerated can flow through and can act on the head section 34 of thepiston 24. The piston 24 is thereby moved away from the spacer cap 16and pushed to the front out of the actuator housing 12.

The base 40 and the opening 42 of the spacer cup 16 form a diaphragm onwhose side facing the pressure element 12 a high-pressure system isformed and on whose side facing the piston 24 a low-pressure system isformed. The pressure build-up in the low-pressure system takes place independence on the diaphragm cross-section, i.e. on the diameter of theopening 42. The diaphragm cross-section therefore represents a controlparameter via which the pressure increase gradient in the low-pressuresystem, and thus ultimately the force acting on the piston 24, can beset.

The displacement of the piston 24 is bounded by a shoulder 46 of theactuator housing 10 which forms an abutment for the head section 34 ofthe piston 24. FIG. 2 shows the piston 24 in an end position in whichthe piston 24 is maximally pushed out of the actuator housing 10 and thehead section 34 abuts the shoulder 46 of the actuator housing 10.

In FIGS. 3 and 4, a second embodiment of the actuator in accordance withthe invention is shown which only differs from the first embodiment inthat grouting is provided for the regularization of the conversion ofthe chemical substances of the pressure element 12 and of the gaspressure created in this process.

The grouting is achieved by a grouting element 48 which surrounds themain section 26 of the piston 24 like a sleeve. The grouting element 48has an outwardly angled section 50 in the region of its front end facingaway from the head section 34. As FIG. 3 shows, the grouting element 48is dimensioned such that the angled section 50 cooperates with theshoulder 46 of the actuator housing 10 in the starting position of thepiston 24 and is in particular supported at said shoulder. The groutingelement 48 is therefore arranged between the head section 34 and theshoulder 46 viewed in the axial direction. The piston 24 is therebyfixed in the actuator housing 10 at its starting position and isprevented from a displacement relative to the actuator housing 10.

The angled section 50 of the grouting element 48 forms a shear sectionwhich has to be sheared off to permit a displacement of the piston 24out of the actuator housing 10. The force required for the shearing offof the shear section 50 can be set by the selection of a correspondingmaterial and/or of a corresponding geometry of the shear section 50,e.g. of the thickness of the shear section 50 and/or of the arrangementof desired break notches. An optimum grouting force and a particularlyuniform realization of the chemical substances can be achieved in thismanner. This permits the setting of a defined gas pressure and thusultimately of a defined ejection force of the piston 24.

FIG. 4 shows the actuator in the triggered state, with the piston 24being in its end position, i.e. being maximally pushed out of theactuator housing 10. As can be seen from the Figure, the head section 34of the piston 24 does not directly abut the shoulder 46 of the actuatorhousing 10 in this case, but only indirectly via the sheared off shearsection 50 disposed therebetween.

So that the movement of the piston 24 in the axial direction is notblocked by the part of the grouting element 48 remaining at the piston24, the inner diameter of the section 52 of the actuator housing 10disposed between the front end face 28 and the shoulder 46 has a widthwhich is larger than an outer diameter of the grouting element 48 in thesheared-off state.

In FIGS. 5 and 6, a third embodiment of the actuator in accordance withthe invention is shown which only differs from the second embodiment inthat the main section 26 of the piston 24 is provided with a knurling54.

The knurling 54 is positioned in a region of the main section 26 in thecenter viewed in the axial direction such that it is pressed into thebore 30 of the front end face 28 of the actuator housing 10 on theejection of the piston 24. The knurling 54 is furthermore made such thatan optimum pressing is present when the piston 24 has reached its endposition, i.e. has been maximally pushed out of the actuator housing 10(FIG. 6).

The knurling 54 pressed into the bore 30 in a slight interference fitand prevents the piston 24 fully pushed out of the actuator housing 10from being able to be pushed back into the actuator housing 10. Theactuator in accordance with the third embodiment therefore represents anirreversible system in which the piston 24 can admittedly be moved outof the actuator housing 10, but cannot be pushed back into it.

The term “irreversible” in this connection is to be understood such thatthe movement of the piston 24 cannot be reversed at least when forcesare applied which occur in the normal use of the actuator. Unlike withthe actuators in accordance with the first and second embodiments, thepiston 24 of the actuator in accordance with the third embodiment cantherefore not easily be pushed back into its starting position.

In FIGS. 7 and 8, a fourth embodiment of the actuator in accordance withthe invention is shown which only differs from the third embodiment inthat, instead of the knurling 54, a friction-retaining sloping surface56 is provided in which the piston 24 jams when moving out. The slopingsurface 56 is formed at the inner side of the actuator housing 10 infront of the shoulder 46, when viewed in the ejection direction of thepiston 24, such that an optimal jamming of the head section 34 isachieved when the piston 24 has reached its end position, i.e. has movedmaximally out of the actuator housing 10 (FIG. 8). As in the thirdembodiment, the completely moved out piston 24 can no longer be movedback into the actuator housing 10 so that it is also an irreversibleactuator in the fourth embodiment.

1. An actuator comprising an actuator element movably supported at anactuator housing, a pyrotechnic pressure element to move the actuatorelement and a control means to control a force exerted onto the actuatorelement by the pressure element to move the actuator element, saidcontrol means including a spacer cup base disposed within said housingintermediate said pressure element and actuator element, and forming afixed, reduced diameter opening operative to establish a pressure dropthereacross, said actuator further comprising a grouting elementarranged between the actuator element and the actuator housing, whereinthe grouting element has a shear section which cooperates with theactuator housing such that a substantial movement of the actuatorelement relative to the actuator housing is only possible after ashearing of the shear section from the grouting element, wherein saidgrouting element has a generally cylindrical portion disposedconcentrically with said piston main portion and extending continuouslyaxially between a leading surface of said piston head section and aradially extending shoulder formed in said actuator housing, saidfrangible radially extending shear section abutting the actuator housingshoulder, wherein the generally cylindrical portion of said groutingelement remains in situ with the piston main portion as it traversesbetween the retracted position and extended position, and wherein thegenerally cylindrical portion of said grouting element carried with thepiston main portion has an outer diameter surface which is axiallyspaced from an adjacent inner diameter surface of said stepped housingbore.
 2. An actuator in accordance with claim 1, wherein the controlmeans comprises a diaphragm.
 3. An actuator in accordance with claim 2,wherein the diaphragm is integrated into a spacer means for the pressureelement.
 4. An actuator in accordance with claim 2, wherein thediaphragm comprises an opening in a spacer cup for the pressure elementand in particular in a base of the spacer cup.
 5. An actuator inaccordance claim 1, wherein grouting is provided for the pressureelement.
 6. An actuator in accordance with claim 1, wherein the actuatorelement is fixed in a starting position by said grouting element.
 7. Anactuator in accordance with claim 1, wherein shear section is supportedat a shoulder of the actuator housing in a starting position of theactuator element.
 8. An actuator in accordance with claim 1, furthercomprising a holding device provided to hold the actuator element in anend position after a movement by the pressure element.
 9. An actuator inaccordance with claim 8, wherein the holding device includes a knurlingof the actuator element which is pressed into a bore of the actuatorhousing on a movement of the actuator element.
 10. An actuator inaccordance with claim 8, wherein the holding device includes afriction-retaining sloping surface of the actuator housing in which theactuator element jams on its movement.
 11. An actuator in accordancewith claim 1, wherein the actuator element is formed by a pistondisplaceably supported in the actuator housing.
 12. A pyrotechnicactuator comprising: a substantially cylindrical actuator housing; anactuator piston supported for limited axial displacement within saidhousing between a retracted position and an extended position, saidactuator piston including a relatively large diameter head sectioncentrally displaced within said housing and a relatively small diametermain section extending axially outwardly therefrom through a steppedbore in said housing; a pyrotechnic pressure element; a spacer cupfixedly mounted within said housing; a pressure element carrier fixedlymounted within said housing and cooperating with said spacer cup todefine a high pressure cavity enclosing said pyrotechnic pressureelement, said spacer cup defining a base having a fixed, relativelysmall diameter opening therein communicating with a low pressure cavitydefined by said base, an adjacent inner diameter surface of said housingand said piston head section to control force exerted on the actuatorpiston; means operative to releasably retain said piston in a retractedposition prior to ignition of said pyrotechnic pressure element; andmeans operative to axially retain said piston in a fully extendedposition following ignition of said pyrotechnic pressure element,wherein said means operative to releasably retain said piston in aretracted position comprises a grouting element having a generallycylindrical portion disposed concentrically with said piston mainportion and extending continuously axially between a leading surface ofsaid piston head section and a radially extending shoulder formed insaid actuator housing, said grouting element having a frangible radiallyextending shear section abutting the actuator housing shoulder such thata substantial movement of the actuator element relative to the actuatorhousing is only possible after a shearing of the shear section from thecylindrical portion of the grouting element, and wherein the generallycylindrical portion of said grouting element remains in situ with thepiston main portion as it traverses between the retracted position andextended position, and wherein the generally cylindrical portion of saidgrouting element carried with the piston main portion has an outerdiameter surface which is axially spaced from an adjacent inner diametersurface of said stepped housing bore.